Finally, the Dev-team has released a working patch to fix the carrier logo issue on unlocked iPhone OS 3.1.2 using UltraSn0w.

All those iPhone users who jailbreak iPhone using PwnageTool 3.1.4 and then Unlock iPhone with UltraSn0w must have noticed the missing Carrier Logo/name at the top-left corner of the screen. The source of this missing Carrier logo problem is the UltraSn0w itself. However it’s just a name displaying bug, nothing wrong with the unlock functionality, which means even after unlocking iPhone with UnltraSn0w your phone works normally, just the carrier logo is missing.